Historical trends in Florida temperature and precipitation   总被引：1，自引：0，他引：1  

Michelle M. Irizarry‐Ortiz  Jayantha Obeysekera  Joseph Park  Paul Trimble  Jenifer Barnes  Winifred Park‐Said  Erik Gadzinski 《水文研究》2013,27(16):2225-2246

Because of its low topographic relief, unique hydrology, and the large interannual variability of precipitation, Florida is especially vulnerable to climate change. In this paper, we investigate a comprehensive collection of climate metrics to study historical trends in both averages and extremes of precipitation and temperature in the state. The data investigated consist of long‐term records (1892–2008) of precipitation and raw (unadjusted) temperature at 32 stations distributed throughout the state. To evaluate trends in climate metrics, we use an iterative pre‐whitening method, which aims to separate positive autocorrelation from trend present in time series. Results show a general decrease in wet season precipitation, most evident for the month of May and possibly tied to a delayed onset of the wet season. In contrast, there seems to be an increase in the number of wet days during the dry season, especially during November through January. We found that the number of dog days (above 26.7 °C) during the year and during the wet season has increased at many locations. For the post‐1950 period, a widespread decrease in the daily temperature range (DTR) is observed mainly because of increased daily minimum temperature (Tmin). Although we did not attempt to formally attribute these trends to natural versus anthropogenic causes, we find that the urban heat island effect is at least partially responsible for the increase in Tmin and its corresponding decrease in DTR at urbanized stations compared with nearby rural stations. In the future, a formal trend attribution study should be conducted for the region. Copyright © 2012 John Wiley & Sons, Ltd.  相似文献   

Paleowind velocity and paleocurrents of pluvial Lake Manly,Death Valley,USA     

Jeffrey R. Knott  Joanna M. Fantozzi  Kelly M. Ferguson  Summer E. Keller  Khadija Nadimi  Carolyn A. Rath  Jennifer M. Tarnowski  Michelle L. Vitale 《Quaternary Research》2012,78(2):363-372

Pluvial lake deposits are found throughout western North America and are frequently used to reconstruct regional paleoclimate. In Death Valley, California, USA, we apply the beach particle technique (BPT) of Adams (2003), Sedimentology, 50, 565–577 and Adams (2004), Sedimentology, 51, 671–673 to Lake Manly deposits at the Beatty Junction Bar Complex (BJBC), Desolation Canyon, and Manly Terraces and calculate paleowind velocities of 14–27 m/s. These wind velocities are within the range of present-day wind velocities recorded in the surrounding area. Sedimentary structures and clast provenance at Desolation Canyon and the Manly Terraces indicate sediment transport from north to south. Lake level, based on the elevation of constructional features, indicates that the hill west of the BJBC was an island and that the BJBC spits formed during simple lake regression. The data are consistent with the hypothesis that the present wind regime (velocity and direction) formed the pluvial Lake Manly features.  相似文献   

Sixty thousand years of magmatic volatile history before the caldera-forming eruption of Mount Mazama, Crater Lake, Oregon     

Heather Michelle Wright  Charles R. Bacon  Jorge A. Vazquez  Thomas W. Sisson 《Contributions to Mineralogy and Petrology》2012,164(6):1027-1052

The well-documented eruptive history of Mount Mazama, Oregon, provides an excellent opportunity to use pre-eruptive volatile concentrations to study the growth of an explosive silicic magmatic system. Melt inclusions (MI) hosted in pyroxene and plagioclase crystals from eight dacitic–rhyodacitic eruptive deposits (71–7.7?ka) were analyzed to determine variations in volatile-element concentrations and changes in magma storage conditions leading up to and including the climactic eruption of Crater Lake caldera. Temperatures (Fe–Ti oxides) increased through the series of dacites, then decreased, and increased again through the rhyodacites (918–968 to ~950 to 845–895?°C). Oxygen fugacity began at nickel–nickel-oxide buffer (NNO) +0.8 (71?ka), dropped slightly to NNO +0.3, and then climbed to its highest value with the climactic eruption (7.7?ka) at NNO +1.1 log units. In parallel with oxidation state, maximum MI sulfur concentrations were high early in the eruptive sequence (~500?ppm), decreased (to ~200?ppm), and then increased again with the climactic eruption (~500?ppm). Maximum MI sulfur correlates with the Sr content (as a proxy for LREE, Ba, Rb, P₂O₅) of recharge magmas, represented by basaltic andesitic to andesitic enclaves and similar-aged lavas. These results suggest that oxidized Sr-rich recharge magmas dominated early and late in the development of the pre-climactic dacite–rhyodacite system. Dissolved H₂O concentrations in MI do not, however, correlate with these changes in dominant recharge magma, instead recording vapor solubility relations in the developing shallow magma storage and conduit region. Dissolved H₂O concentrations form two populations through time: the first at 3–4.6 wt% (with a few extreme values up to 6.1 wt%) and the second at ≤2.4 wt%. CO₂ concentrations measured in a subset of these inclusions reach up to 240?ppm in early-erupted deposits (71?ka) and are below detection in climactic deposits (7.7?ka). Combined H₂O and CO₂ concentrations and solubility models indicate a dominant storage region at 4–7?km (up to 12?km), with drier inclusions that diffusively re-equilibrated and/or were trapped at shallower depths. Boron and Cl (except in the climactic deposit) largely remained in the melt, suggesting vapor–melt partition coefficients and gas fractions were low. Modeled Li, F, and S vapor–melt partition coefficients are higher than those of B and Cl. The decrease in maximum MI CO₂ concentration following the earliest dacitic eruptions is interpreted to result from a broadening of the shallow storage region to greater than the diameter of subjacent feeders, so that greater proportions of reservoir magma were to the side of CO₂-bearing vapor bubbles ascending vertically from the locus of recharge magma injection, thereby escaping recarbonation by streaming vapor bubbles. The Mazama melt inclusions provide a picture of a growing magma storage region, where chemical variations in melt and magma occur due to changes in the nature and supply rate of magma recharge, the timing of degassing, and the possible degree of equilibration with gases from below.  相似文献   

The influence of citric acid,EDTA, and fulvic acid on U(VI) sorption onto kaolinite     

Michelle Barger  Carla M. Koretsky 《Applied Geochemistry》2011

Uranium(VI) sorption onto kaolinite was investigated as a function of pH (3–12), sorbate/sorbent ratio (1 × 10^?6–1 × 10^?4 M U(VI) with 2 g/L kaolinite), ionic strength (0.001–0.1 M NaNO₃), and pCO₂ (0–5%) in the presence or absence of 1 × 10^?2–1 × 10^?4 M citric acid, 1 × 10^?2–1 × 10^?4 M EDTA, and 10 or 20 mg/L fulvic acid. Control experiments without-solids, containing 1 × 10^?6–1 × 10^?4 M U(VI) in 0.01 M NaNO₃ were used to evaluate sorption to the container wall and precipitation of U phases as a function of pH. Control experiments demonstrate significant loss (up to 100%) of U from solution. Although some loss, particularly in 1 × 10^?5 and 1 × 10^?4 M U experiments, is expected due to precipitation of schoepite, adsorption on the container walls is significant, particularly in 1 × 10^?6 M U experiments. In the absence of ligands, U(VI) sorption on kaolinite increases from pH ～3 to 7 and decreases from pH ～7.5 to 12. Increasing ionic strength from 0.001 to 0.1 M produces only a slight decrease in U(VI) sorption at pH < 7, whereas 10% pCO₂ greatly diminishes U(VI) sorption between pH ～5.5 and 11. Addition of fulvic acid produces a small increase in U(VI) sorption at pH < 5; in contrast, between pH 5 and 10 fulvic acid, citric acid, and EDTA all decrease U(VI) sorption. This suggests that fulvic acid enhances U(VI) sorption slightly via formation of ternary ligand bridges at low pH, whereas EDTA and citric acid do not form ternary surface complexes with the U(VI), and that all three ligands, as well as carbonate, form aqueous uranyl complexes that keep U(VI) in solution at higher pH.  相似文献   

Environmental assessment of water from a uranium mine (Caldas,Minas Gerais State,Brazil) in a decommissioning operation   总被引：1，自引：1，他引：0  

Michelle Burato Campos  Heliana de Azevedo  Marcos Roberto Lopes Nascimento  Cláudio Vítor Roque  Suzelei Rodgher 《Environmental Earth Sciences》2011,62(4):857-863

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Impacts of climate, lake size, and supra- and sub-permafrost groundwater flow on lake-talik evolution, Yukon Flats, Alaska (USA)   总被引：3，自引：2，他引：1  

Tristan P. Wellman  Clifford I. Voss  Michelle A. Walvoord 《Hydrogeology Journal》2013,21(1):281-298

In cold regions, hydrologic systems possess seasonal and perennial ice-free zones (taliks) within areas of permafrost that control and are enhanced by groundwater flow. Simulation of talik development that follows lake formation in watersheds modeled after those in the Yukon Flats of interior Alaska (USA) provides insight on the coupled interaction between groundwater flow and ice distribution. The SUTRA groundwater simulator with freeze–thaw physics is used to examine the effect of climate, lake size, and lake–groundwater relations on talik formation. Considering a range of these factors, simulated times for a through-going sub-lake talik to form through 90 m of permafrost range from ～200 to >?1,000  years (vertical thaw rates <?0.1–0.5  m?yr^?1). Seasonal temperature cycles along lake margins impact supra-permafrost flow and late-stage cryologic processes. Warmer climate accelerates complete permafrost thaw and enhances seasonal flow within the supra-permafrost layer. Prior to open talik formation, sub-lake permafrost thaw is dominated by heat conduction. When hydraulic conditions induce upward or downward flow between the lake and sub-permafrost aquifer, thaw rates are greatly increased. The complexity of ground-ice and water-flow interplay, together with anticipated warming in the arctic, underscores the utility of coupled groundwater-energy transport models in evaluating hydrologic systems impacted by permafrost.  相似文献   

pH variability off Goa (eastern Arabian Sea) and the response of sea urchin to ocean acidification scenarios     

Suhas S. Shetye  Hema Naik  Siby Kurian  Damodar Shenoy  Nandakumar Kuniyil  Michelle Fernandes  Afreen Hussain 《Marine Ecology》2020,41(5):e12614

The increasing atmospheric CO₂ concentration in the last few decades has resulted in a decrease in oceanic pH. In this study, we assessed the natural variability of pH in coastal waters off Goa, eastern Arabian Sea. pH_T showed large variability (7.6–8.1) with low pH conditions during south-west monsoon (SWM), and the variability is found to be associated with upwelling rather than freshwater runoff. Considering that marine biota inhabiting dynamic coastal waters off Goa are exposed to such wide range of natural fluctuations of pH, an acidification experiment was carried out. We studied the impact of low pH on the local population of sea urchin Stomopneustes variolaris (Lamarck, 1816). Sea urchins were exposed for 210 days to three treatments of pH_T: 7.96, 7.76 and 7.46. Our results showed that S. variolaris at pH_T 7.96 and 7.76 were not affected, whereas the ones at pH_T 7.46 showed adverse effects after 120 days and 50% mortality by 210 days. However, even after exposure to low pH for 210 days, 50% organisms survived. Under low pH conditions (pH_T 7.46), the elemental composition of sea urchin spines exhibited deposition of excess Sr²⁺ as compared to Mg²⁺ ions. We conclude that although the sea urchins would be affected in future high CO₂ waters, at present they are not at risk even during the south-west monsoon when low pH waters reside on the shelf.  相似文献   

A new hematite formation mechanism for Mars     

Michelle E. MINITTI  Melissa D. LANE  Janice L. BISHOP 《Meteoritics & planetary science》2005,40(1):55-69

Abstract— The origin of hematite detected in Martian surface materials is commonly attributed to weathering processes or aqueous precipitation. Here, we present a new hematite formation mechanism that requires neither water nor weathering. Glass‐rich basalts with Martian meteorite‐like chemistry (high FeO, low Al₂O₃) oxidized at high (700 and 900 °C) temperatures in air and CO₂, respectively, form thin (<1 μm) hematite coatings on their outermost surfaces. Hematite is manifested macroscopically by development of magnetism and a gray, metallic sheen on the glass surface and microscopically by Fe enrichment at the glass surface observed in element maps. Visible and near‐infrared, thermal infrared, and Raman spectroscopy confirm that the Fe enrichment at the oxidized glass surfaces corresponds to hematite mineralization. Hematite formation on basaltic glass is enabled by a mechanism that induces migration of Fe²⁺ to the surface of an oxidizing glass and subsequent oxidation to form hematite. A natural example of the hematite formation mechanism is provided by a Hawaiian basalt hosting a gray, metallic sheen that corresponds to a thin hematite coating. Hematite coating development on the Hawaiian basalt demonstrates that Martian meteorite‐like FeO contents are not required for hematite coating formation on basalt glass and that such coatings form during initial extrusion of the glassy basalt flows. If gray hematite originating as coatings on glassy basalt flows is an important source of Martian hematite, which is feasible given the predominance of igneous features on Mars, then the requirement of water as an agent of hematite formation is eliminated.  相似文献   

Radiation transfer of gyrosynchrotron emission in stellar environments     

Michelle C. Storey 《Solar physics》1996,168(2):435-447

Non-thermal radio emission has been detected from several kinds of active stars. Polarization and intensity measurements of the quiescent (i.e. non-flaring) emission indicate gyrosynchrotron emission. A three-dimensional magnetic field model for the stellar field is presented and the gyrosynchrotron intensity and polarization emerging from such a model is calculated and compared with observations. Model spectra agree well with observations. Model polarization results indicate that the emission region is more complex than the simple model and may indicate the presence of multipole components in the field, small loops of flux near the stellar surface and significant energy loss in the radiating electron distribution over time.  相似文献   

Eolian controlled modification of the martian south polar layered deposits     

Michelle R. Koutnik  Shane Byrne  Anthony D. Toigo 《Icarus》2005,174(2):490-501

Data from the Mars Orbiter Laser Altimeter (MOLA) and Mars Orbiter Camera (MOC) aboard the Mars Global Surveyor (MGS) mission and the Thermal Emission Imaging System (THEMIS) aboard the Mars Odyssey mission have revealed unique surface features in a particular region of the South Polar Layered Deposits (SPLD). The dominant morphology is large-scale quasi-parallel grooves that extend for hundreds of kilometers with only tens of meters of vertical relief, that we have termed here the “Wire Brush” terrain. The grooves are also transected by disjointed, yet roughly continuous, low-relief sinuous ridges that cross roughly perpendicular to the trend-direction of the large-scale grooves and show only tens of meters of relief. We interpret these ridges to be eroded remnants of folded layers. At the northern end of the large-scale grooves there are non-symmetric mounds. They are frequently preceded by a significant depression and/or trailing grooves that are parallel to the Wire Brush trend. We find that a two-stage process involving winds that intermittently remove a low-density crust exposing the underlying ice to ablation is the interpretation that best explains the multitude of features observed here. These features appear to be currently inactive indicating higher winds in previous epochs.  相似文献